An investigation of the cross-bridge cycle using ATP analogues and low-angle X-ray diffraction from glycerinated fibres of insect flight muscle

The interdigitating filament arrays of muscle contain as their major components the proteins actin and myosin. Globular actin molecules aggregate to form the “thin” filaments. Myosin molecules consist of fully α-helical tails and enzymatically active heads. The molecules spontaneously aggregate to form bipolar filaments (the “thick” filaments) with the heads protruding to form the “cross-bridges”. Two heads may constitute one cross-bridge. The interaction between actin and myosin is mediated by the cross-bridges. By limited proteolytic digestion the enzymatically active fragments of myosin S1 (single heads) and HMM (two heads with a length of tail) may be prepared. The heads (S1) are joined to the tails by a more flexible part of the tail known as the S2 region. (For details and references see Huxley, this volume.)Actin Filament Adenylate Kinase Layer Line Myosin Filament Myosin Molecul